The present invention generally relates to the field of telecommunications, and more particularly, is directed to a pay telephone system which does not require the use of dedicated facilities in a telephone company local central office for each phone, and which provides a more efficient means of utilizing existing facilities for placing calls from public telephones while concurrently expanding the possible range of services and convenience to the caller.
FIG. 1 is a block diagram showing a conventional switched telephone network interconnecting several metropolitan areas. The switching centers in each area are virtually the same in terms of function and differ only in number depending on the size of the area served and number of telephone set subscribers. The number of switching centers for each city in FIG. 1 is shown as being equal merely for purposes of simplicity.
With reference to FIG. 2, the switching centers for a typical metropolitan area, i.e., the city of Dallas shown in FIG. 1, will be explained. Each subscriber telephone set is connected to a local central office 1, via a subscriber loop. When a subscriber wishes to place a local call and dials the seven digit telephone number, the first three digits identify the central office which serves the party being called and the last four digits identify the particular telephone within that central office. For example, when a subscriber served by central office 1a wishes to call a party served by central office 1b, central office 1a recognizes the first three digits of the telephone number as identifying central office 1b. The subscriber's telephone is then connected through central office 1a to central office 1b via an interoffice trunk. Central office 1b then uses the last four digits of the telephone number to identify the particular subscriber loop to which the party being called is connected and connects and rings that party's telephone.
Each central office in the system is also connected to a tandem office 2. The purpose of tandem office 2 is to simply switching between central offices and is itself not directly connected to any subscriber lines. Tandem offices located in central places provide more efficient switching by combining small amounts of traffic from the various central offices and routing the combined traffic over a common trunk to the required destination. Thus, direct interconnection of all central offices may be eliminated or the number of interoffice trunks greatly reduced.
When a subscriber wishes to make a long distant call, the call is routed from the subscriber's central office to a toll office 3. Toll office 3 is interconnected by long distance lines to toll offices in other metropolitan areas across the country. Depending on the amount of long distance traffic, a caller in New York wishing to call, for example, Los Angeles may be routed directly to Los Angeles or via alternate routes, such as through Washington, D.C. and Dallas as shown in FIG. 1.
As shown in FIG. 2, each central office 1 also services a plurality of public pay telephones via dedicated pay telephone lines. When a caller uses a pay telephone, the central office which serves the telephone waits to receive tones transmitted from the telephone which indictes that the initial rate has been deposited in the telephone. The dialed number is then screened by the central office and if the screening indicates that the call is local station-to-station and the local rate has not been satisfied, the call is routed to a central office announcement which tells the caller the amount of the deposit he must make to complete the call and to hang-up and try again. If the call was recognized as being a long distance call or was prefixed by a "0" (indicating that the caller wished alternate billing treatment and did not wish to pay by coin), then the call is routed by trunk lines to a traffic service position systems shown as TSPS 4 in FIG. 2. TSPS 4 is normally located in a tandem office and serves a plurality of local offices 1. It receives and processes the dialed telephone number. If the telephone number is not prefixed by "0", then TSPS 4 calculates the initial charge for the call based on the locations of the calling phone and the dialed number. TSPS 4 then waits for tones to be transmitted from the pay telephone indicating that the initial deposit requested was satisfied. When this signal is received, TSPS 4 then redials the call through toll office 3. This of course means that all nonlocal pay telephone calls must be "hauled" to the tandem office for processing and are then transmitted into the network from that point.
Also known in the prior art are pay telephones which include credit card readers which permit the telephone call to be charged to the caller's telephone company account. Such telephones are indicated by reference No. 5 in FIG. 2 and are also connected to dedicated pay telephone loops from a telephone company central office. When one of these types of pay telephones is used, the call is not forwarded to TSPS 4 but rather is forwarded to call processor 6. Call processor 6 contains the credit card number and verifies that the credit card is valid and that the caller's account is in good standing from information stored in credit card authorization network 7. If the card is valid and the caller's account is in good standing, call processor 6 creates a billing record for later debiting of the caller's account then redials the number back into the switching network and times the call through to completion. The billing information is then later retrieved and used for pricing and billing of the call.
The invention of the telephone and the complex switching network which makes it useful has permitted a quantum leap in man's ability to communicate. Unfortunately, the economics of capital investment and the demand for telephone service has made it difficult to implement improvements in the telephone system infrastructure as rapidly or with as much variety as technology permits. The presentday switched telephone network and network architecture evolved at a time when there was only one long distance carrier. Thus, there was no need to design the system to accommodate other carriers or to provide telephone subscribers with the ability to select a particular carrier. However, recent changes in the telecommunications industry have lead to the formation of a number of long distance carriers from which the consuming public may select for long distance telephone service. Unfortunately, the present switched telephone network does not permit the public or the telephone owner to select the long distance carrier of its choice in every situation. This is especially true with respect to pay telephones which presently rely on special telephone lines from a telephone company central office. The present invention overcomes these problems.